To perform virtual server cloning, an administrator installs and configures a reference system. This reference system is then shutdown, and a copy is made of the reference system. The copy can either be kept in an image form for later use, or the copies can be made directly to the target storage, for example by using a disk duplicator. The copy is often block-based, or for more sophisticated tools, may be file based. The copied system is then booted and customizations are manually made to that system to differentiate it. Typically, when a manual method is used for cloning servers, the desired installation and configuration is not documented. The manual method for cloning is expensive due to the cost of labor, does not scale well, and tends to be error prone.
Changes to a virtual server's installation and/or configuration are part of the normal server management lifecycle. Typically, the way to propagate a change made to a virtual server's image or configuration is to redeploy the image to the affected virtual server. This is a resource intensive task, as it will often involve writing tens to hundreds of gigabytes of data, depending on the size of the storage devices and the number of servers. This is a relatively expensive process for implementing minor changes. Alternatively, an administrator could make the changes manually to each affected server, however, this process does not scale and tends to be error prone.
Another conventional approach for changing the configuration of a virtual server is installing a host agent on the virtual server to receive instructions from a managing device to change or update a particular configuration property. However, this approach consumes resources used by the virtual server. Also, in a secured environment, this approach requires extra network configurations to provide a secure communications channel between the managing device and the virtual server. Therefore, this may present a potential security hazard, and adds another element of complexity in the system.
If an image of a reference virtual server needs to be copied to multiple virtual servers, the reference virtual server can be cloned by copying the image and deploying the image to the multiple servers. The deploy operation is typically done sequentially. That is, the image is read, decompressed, and written to one of the virtual servers. When done, the next virtual server is deployed, again, by reading, decompressing, and writing the same data.
Usually, the only difference for subsequent virtual servers being deployed is the destination of the data. Consequently, virtual server cloning is an expensive operation due to the amount of data that must be read and written.